1. Field of the Invention
The present invention relates to devices for determining the fluid flow in a conduit and, in particular, to devices for determining volumetric flow in partially-filled closed conduits.
2. Description of the Prior Art
It is known that to most accurately measure the volumetric liquid flow or rate of flow in a partially liquid-filled conduit, it is necessary to measure the velocity of the liquid and the cross-sectional area of the fluid-filled portion of the conduit and then multiply the two together to determine volumetric flow. If the shape and dimensions of the conduit are known, it is only necessary to measure the velocity of the liquid and the height of its level in the conduit. In special cases, such as sewer pipes operating under gravity flow, a number of well-known equations, such as the Manning equation, will permit approximate flow measurement by simply measuring the depth of the liquid. However, for increased accuracy, both depth and velocity are typically measured and the flow equations solved.
Measuring volumetric flow in partially-filled closed conduits is more complicated and, in the past, it has been necessary to penetrate the pipe wall and to insert measuring transducers. One prior apparatus for accomplishing this is disclosed in U.S. Pat. No. 4,083,246. However, that type of prior flowmeter requires access to the interior of the conduit by the measuring transducers, requiring openings in the conduit. This is expensive and is conducive to leakage at the penetrations. Also, contamination of the transducers due to suspended particulates in the liquid stream is common, particularly in waste water applications, decreasing transducer accuracy. Furthermore, such prior flowmeters for partially filled conduits have been permanently or semi-permanently mounted in or adjacent to the conduit and have not been readily relocatable.